Lubricating oil composition



metal surfaces of the engine.

Patented Mar. 1d, U NE STATES PATENT OFFICE Thomas, Jr., Stamford,

-- (1 Company, New York, N. Y.,

crican a corporation of Maine No Drawing. Application so. ,t-

Conm, assdgnors to Serial No. 431,866

This invention relates to a new and useful composition of matter; more particularly a composition comprising a lubricating oil and a zinc salt of diamyl dithiophosphate.

in our 'copending application Serial No. 401,960 filed July 11, 19 1, of which this'is a continuation-in-part, it was pointed out that conventional types of lubricating oils when subjected to high operating temperatures for long periods of time tend to decompose with the formation of com plex and objectionable oxidation and decomposh tion products. Under the high temperature conditions obtaining inengines, particularly in bus, tractor, Diesel and aeroplane engines in heavy duty service, these decomposition products polymerize to form lacquer-like deposits on or between the moving parts causing these parts to stick. 'Even larger quantities, of polymerization roducts remain dispersed in the partly oxidized crankcase oil, and are precipitated to form a sludge when the engine cools or when freshoil is added. These precipitated sludges become caked on heated metal surfaces and cut down the eiiective life of the engine.

As pointed out in our .copending application referred to above the lubricating oil oxidation and decomposition products are corrosive and attack modern type alloy bearings such as copper-lead, silver-cadmium, nickel-cadmium, and the like which are widely employed in internal combustion engines. To disperse the sludge, remove the deposits and prevent corrosion many different types of materials have been tried with more or less success. Compoundshaving a detergent action such as calcium stearate, calcium naphthenate and the like have been employed and while these compounds are effective. as detergents they do not prevent corrosion of the alloy bearings. Certain anti-corrosion agents such as triphenyl phosphite and sulfurized sperm oil have been employed to combat the corrosive effects of the acidic oxidation products of the oil but have no detergent action. Ordinarily mixtures'of detergents and anti-corrosion agents do not perform satisfactorily together since the function of a corrosion inhibitor is to cover the corrodible metal surfaces with apassivating film but the detergent tends to remove it thus producing a clean metal surface subject to corrosion.

In our above-mentioned copending application we disclose that certain heavy metal salts of dithiophosphate esters may be employed in lubricating oils to perform thedual function of preventing corrosion and sludge formation with its tendency to form lacquer-like deposits on the In that application we stated that we prefer the alkaline earth metal salts of dialkyl dithiophosphates because of their excellent detergent moperties. We also stated that we prefer those dialkyl dithiophos- 60 is true because .alkyl groups of only {carbon phates in which each almgroup contains. 8, l0, 1%, 14 or more carbon atoms. The preference for these long chain dialkyl dithiophosphates was based principall? upon the greater ease with which these compounds could be dissolved in lubricating oils. In fact, it has become generally recognised among chemists that organic compounds should have one or more long chain alkyl groups preferably of about 12 carbon atoms to render them sufilciently soluble in lubricating oil to boot practical value. ,The difliculty with which alkaline earth metal short chain dialkyl dithiophosphates dissolved in lubricatingv oils was illustrated in our above-mentioned case when we stated that we had succeeded in incorporating substantial amounts, even greater than 3%, of barium and other heavy metal salts of the lower diailnvl dithiophosphates by first admixing or dissolving them in metal salts of 2,4- diamylphenol sulfides which act as mutual solvents. Ordinarily barium diamyl dithiophosphate is soluble only to the extent of about 02-05% in ordinary lubricating oil.

Easyblending of lubricating oil additives with hydrocarbon lubricating oils is of considerable importance from a practical standpoint and accordingly while certain of the lower dialkyl dithiophosphates can be blended with lubricating oils by the employment of special techniques the difliculty and additional expense of doing so does not warrant their use. It is also customary in the art to prepare, ship and store these additives in the form of about 50% solutions of the additive in lubricating oil so that the blender need onLv pour the additive composition into the lubricating oil with suitable stirring. Additives-of difllcult solubility cannot be employed in-this manner and consequently are under a serious handicap zinc diamyl dithiophosphate and dissolved in.

an'equal weight of 30-W lubricating oil without difficulty and the solution has remained perfectly clear" and stable upon standing over a long period of time. The reason for the unexpected- 1y high solubility of this particular compound is not altogether clear, but the importance of this Property is evident.

Although it has been heretofore believed that the most advantageous dlthiophosphoric acid esters for use as constituents of lubricating oil additives are those containing the alkaline earth metals, we have found that equally good and in some. cases better results are obtained with the zinc-salt of diamyl dithiophosphoric acid, This toluene were mixed and 135 phorus and sulfur, which are the active anticorrosion agents, and also a larger molecular proportion of the metal, i. e. zinc, than ispresent in the alkaline earth metal salts of higher molecular weight. Detergent and anti-corrosion efiects comparable with those obtained by the use of an alkaline earth metal such as barium are therefore obtained by the compounds of our presentinvention.

Although we may prepare our additives by reacting P285 with any straight or branched chain primary, secondary or tertiary amyl alcohol we prefer touse a commercially obtainable mixture of amyl alcohols known in the trade as Pentasol. This mixture of amyl alcohols is prepared by chlorinat-ing a mixture of normal andisopentane which product is then hydrolyzed to the corresponding amyl alcohols. The various amyl. alcohols present inthis mixture are as follows:

CHsCHzCI-IzCl-IzCI-IaOH (CH3) zCHCI-IzCHzOI-li CH3CH2CH(CH3) zCHzOH CHsCHzCHzCHOI-ICH:

and

CHsCI-IzCI-IOHCHzCI-Ia The three primary alcohols predominate. The mixture has an initial boiling point of 112 C. and a final boiling point of about 140 C., a refractive index at C. of 1.4092 and a specific gravity of 0.810 to 0.820. Where the word amyl is recited in the appended claims'this is intended to include any of the amyl alcohols or mixtures, thereof described herein.

The preparation of our zinc diamyl dithiophosphates will now be described: 745 grams of the Pentasol mixture described above and 516 grams of finely ground P2S5 (10% excess) were heated for two hours at 85100 C. with stirring at which time almost all of the P255 had disappeared and evolution of H23 from the reaction mixture had practically stopped. The reaction mixture was cooled and the unreacted P285 allowed to settle. 1039 g. of the di-Pentasol dithiophosphate, decanted from the unreacted P285, 343 cc. of 95% ethyl alcohol and 701 cc. of

g. of zinc oxide added in g. portions with stirring while maintaining the temperature between and C. until the reaction mixture was neutral to Congo red paper. The solution was then filtered and evaporated under a vacuum. until about 75% of the solvent had been removed. 1135 g. of a 30-W grade lubricating oil was then blended with the zinc diamyl dithiophosphate while continuing the vacuum evaporation to remove the remainder of the solvent. A yield of 2268 g. of a clear blend containing about of zinc diamyl di- 'thiophosphate,

{ CsHu I l. csnuo -2 was obtained.

The effectiveness of the above-described zinc salt of diamyl dithiophosphoric acid in lubricating oils as a detergent and anti-corrosion conlubricating oil stituent is demonstrated by the following results obtained by subjecting a #30-W grade Mid-Continent solvent extracted oil containing 0.25% of zinc diamyl dithiophosphate to the standard Underwood oxidation test. This test consists in heating 1500 cc, of the'oil to 325 C, and continuously spraying a portion of the heated oil against a 3 inch by 10 inch freshly sanded copper baille, a freshly sanded copper-lead alloy hearing and a freshly sanded silver-cadmium alloy bearing, for five hours while permitting free circulation of air. Samples of the oil are then examined for A. P. I. gravity, neutralization number, naphtha insolubles and bearing loss due to the effects of corrosion. The neutralization number indicates the formation of acids resulting from oxidation of the oil and the A. P. I.

gravity also indicates the decomposition of the oil during the test, the lower value indicating the greater degree of decomposition. The particular oil employed in these tests, being of the solvent refined type, was particularly resistant to sludge formation. A sample of the same oil to serve as a basis of comparison was also tested at the same time and under the same conditions. The samples contained 0.116% of iron naphthenate as required by the test. were as follows:

These results show the very great effectiveness of zinc diamyl dithiophosphates in preventing oxidation and decomposition of the oil and corrosion of alloy bearings under the extremely drastic conditions of the Underwood test.

Zinc diamyl dithiophosphate was also tested by the well known Catalytic Indiana test. This test is conducted in an apparatus consisting of.a constant temperature bath maintained at 341 F. in which a number of large glass test tubes are immersed. 300 cc. samples of the oil under test are poured into these-tubes and air is bubbled through the oil at the rate of 10 liters per hour. In order to reproduce the conditions prevailing in the crankcaseof an engine, weighed strips of a copper-lead alloy are suspended in the samples.

Bearing corrosion tests are determined by weighing the strips after 70 hours immersion. The results of this test were as follows:

1 Gained.

Results obtained from this test were unusual in that the bearing showed no loss whatever in weight and in fact gained slightly. The walls of The results the test tube containing the oil treated with zinc diamyl dithiophosphate were clean after the test thus showing the detergent action of'the added salt. The results of this test confirm the results obtained by the previously described Underwood test.

Because of the very high efi ectiveness gf these zinc diamyl dithiophosphates as detergents and I anti-corrosion agents it is necessary to employ but very small amountsof them in the" oil. In lubricating oils intended for an ordinary service where extremely high temperatures occur only occasionally 0.10.8% of the zinc diamyl dithiophosphate is suflicient. In heavy duty service it is generally advisable to use a little more as for example 0.53% in the oil. They may, of course, be used with other materials added to the oil for specific purposes and form particularly heat-stable lubricating oils in combination with or more of their weight of an alkaline earth salt of 2,4-diallwl diphenol monosulfide, such as barium 2,4-diamyl diphenol monosulfide.

Although as pointed out before one of the advantageous features of our new lubricating oil additive is its high solubility in lubricating oils enable us to prepare solutions for distributionto the trade containing from 30-60% or more by weight of the zinc diamyl dithiophosphate. However, because of the ease with which they may be dissolved in lubricating oils it is a simple mat ter for the blender to disperse them directly in the oil without previous treatment and without the aid of mutual solvents, etc. Accordingly the appended claims-are intended to cover both the improved lubricating oil composition containing our zinc diamyl dithiophosphates a well as blends of the same containing as high as or more of the salt in conventional type lubricating oils.

What we claim is:

. 1. A lubricating oil composition comprising at least 0.1% by weight of a zinc salt of diamyl dithiophosphoric acid and a lubricating oil.

2. A lubricating oil composition comprising at least 0.1% by weight of a zinc di-Pentasol dithiophosphate and lubricating oil.

3. A lubricating oil composition containing zinc diamyl dithiophosphate in amounts of from ill-3.0% and a hydrocarbon lubricating oil.

4. A composition adapted to be blended with hydrocarbon lubricating oils which comprises a 50% solution. of zinc diamyl dithiophosphate in lubricating oil.

5. A lubricating oil composition comprising at least 0.1% by weight of zinc diamyl dithiophosphate, an alkaline earth salt of 2,4-diaikyl diphenol monosulilde, and a lubricating oil.

6. A lubricating oil composition comprising at least 0.1% by weight of zinc diamyl dithiophos phate and a barium salt of 2,4-diamyl diphenol monosulfide and a major proportion of a lubrieating oil. I

ELMER W. COOK. WILLIAM D. THOMAS, Ja 

